PHYLUM MOLLUSCA 223 



are practically without special sense organs (except those 

 for balancing the body and for testing the surrounding 

 water), and depend largely on reflexes in their daily activi- 

 ties, but the scallops (Pecten) which swim actively have 

 a double row of eyes around the edges of the mantle. The 

 snails are somewhat more active than clams, and have 

 simple eyes, organs of taste, and other sensory structures, 

 but are at best rather slow. The most active molluscs are 

 the cephalopods, and they show the most elaborate sen- 

 sory organs: well-developed eyes, balancing organs, taste 

 organs, etc. 



The mental powers of all molluscs are very limited. As 

 would be expected from their superior sensory equipment, 

 the cephalopods excel other members of the group. They 

 are able to see and pursue their prey, elude their enemies, 

 and carry on other activities which are impossible for the 

 sluggish clams and snails. One investigator taught a squid 

 to take food from a hole in a glass tube, and the food was 

 extracted more quickly after some experience had been 

 gained. 



